Orthodontic brackets are used in orthodontic treatments for moving one or more teeth from an initial position (sometimes referred to as malposition or malocclusion) to a desired position in a patient's dentition. For example by an orthodontic treatment the patient's teeth may be moved such that their labial sides are aligned with each other to achieve or maximize an aesthetically pleasant appearance of the overall dentition. Further in some cases one or more teeth may be moved to correct a malocclusion. The movement of teeth is typically achieved by a pre-biased elastic archwire which is attached via brackets to the teeth, and which applies a force to the teeth toward the desired position over a longer time period. The ends of orthodontic archwires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the upper and lower dental arches.
In many types of orthodontic techniques, the precise position of the appliances on the teeth is an important factor for helping to ensure that the teeth move to their intended final positions. For example, one common type of orthodontic treatment technique is known as the “straight-wire” technique, where the archwire lies in a horizontal plane at the conclusion of treatment. If, for example, a bracket is attached to the tooth at a location that is too close to the occlusal or outer tip of the tooth, the orthodontist using a straight-wire technique will likely find that the tooth in its final position is unduly intruded. On the other hand, if the bracket is attached to the tooth at a location closer to the gingiva than is appropriate, it is likely that the final position of the tooth will be more extruded than desired.
So-called treatment planning systems have been used to determine the desired position of the teeth in a computer simulation in advance of any actual treatment. Such a planning system helps for example for avoiding collisions between the teeth and brackets in tooth positions outside the initial position, and further allows for the brackets and the archwire to be designed and arranged to match with a variety of clinical situations, for example with the position of the teeth in the initial position, in the desired position, and positions between. In particular for lingual brackets such treatment planning is widely used. Lingual brackets often have a customized design individually for every tooth and patient because, other than the labial surfaces of a tooth, the lingual surfaces greatly vary in shape relative to each other so that a “one size fits all” bracket shape typically cannot be used. Some treatment planning systems also allow for designing such customized brackets which precisely match a tooth surface and the required clinical situations of a patient. Accordingly customized brackets typically have to be precisely placed at positions on the teeth which are predetermined during the treatment planning. For facilitating a precise placement of the brackets on a patient's teeth and for the orthodontist's reference, the brackets are often provided prepositioned on a plaster model replicating the patient's teeth.
Such a plaster model on which the brackets are placed is sometimes used in orthodontics to make a so-called transfer tray for facilitating the placement of the bracket on a patient's teeth. A transfer tray typically is adapted to hold a complete set of brackets at the predetermined position and allow the brackets to be placed and bonded on the teeth in one step.
In general, indirect bonding techniques have involved the use of a transfer tray having a shape that matches the configuration of at least part of a patient's dental arch. A set of appliances such as brackets are releasably connected to the tray at certain, predetermined locations. Adhesive is applied to the base of each appliance, and the tray is then placed over the patient's teeth until such time as the adhesive hardens. Next, the tray is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the tray are now bonded to the respective teeth at their intended, predetermined locations.
For example, as disclosed in WO 01/80761, treatment planning software virtually superimposes brackets on teeth to generate a three-dimensional model comprising the three-dimensional tooth objects plus the virtual brackets at their intended locations. This three-dimensional model is supplied to a stereo lithography (SLA) instrument for manufacturing a plastic model of the teeth with the brackets superimposed thereon. A thermoplastic foil is placed above the SLA model and the model and foil are placed within a pressure chamber. The chamber is pressurized so that the foil envelops the dentition and the brackets. The foil thus obtains small indentations where the brackets can be located.
EP Application No. 1 2196 586 describes a method of making a transfer tray from an integrated physical mockup. The integrated physical mockup represents a shape composed of the positive shape of a patient's dental arch and the positive shape of a set of bracket analogs. The bracket analogs may substantially correspond in shape to the shape of the desired orthodontic bracket, but may include less substantial or fewer undercuts, grooves, and recesses than said corresponding bracket body. The shape of the dental arch and the set of analogs can cooperate to form one contiguous piece, which can allow for creation of a transfer tray in which brackets can be removably placed and positioned without substantially damaging the transfer tray. Further a transfer tray prepared by use of the integrated physical mock up can allow precise positioning of the brackets, while permitting removal of the brackets at relatively low forces.